1. Field of the Invention
The present invention relates to copper alloys having improved processability. More particularly, the ductility of the alloys is increased by spray casting permitting greater cold rolling reductions.
2. Description of the Background
Alloying elements are typically added to copper to increase the yield strength, improve corrosion resistance, increase the resistance to thermally induced softening or to impart the metal with other desirable properties. The alloying is usually accomplished by dissolving the desired concentration of alloying elements within molten copper. When the mixture cools, an alloy having the desired concentration of elements is formed. For many combinations of elements, a non-uniform distribution of alloying elements occurs during cooling. The localized concentration of additives is known as microsegregation. This phenomenum is undesirable. The segregated regions reduce the processability and the electrical conductivity of the bulk alloy.
One alloy system which is prone to microsegregation is a copper base alloy containing nickel, tin and silicon. The alloy has high strength and excellent mechanical properties. The electrical conductivity is about 5% to about 10% that of pure copper. While low compared to copper, the conductivity is comparable to other alloys having similar mechanical properties. These alloys typically find use as spring type connectors. The spring temper of the connector must be retained following numerous insertion and removal cycles.
To date, copper-nickel-tin-silicon alloys have met with limited commercial acceptance due to limited processability. The alloy is subject to severe microsegregation. A brittle nickel-tin intermetallic phase segregates from the alloy matrix during cooling severely reducing the ductility of the bulk alloy.
The usual method of minimizing microsegregation is to solutionize the alloy. The alloy is heated to a temperature sufficient to dissolve the intermetallic phase into the alloy. The solutionized alloy is then rapidly solidified by quenching to minimize the growth of the intermetallic phase. Rapid solidification is intended to freeze in the solutionized microstructure. It is inadequate for copper base alloys prone to microsegregation. The intermetallic phase forms so quickly that even when solutionization is followed by quenching, the alloy exhibits edge cracking during cold rolling. The alloy also has limited hot rolling processability.